1. Field of the Invention
This invention relates to wheel probes used for ultrasonically inspecting a component, and in particular to wheel probes used in ultrasonic pipe inspection apparatus that can be inserted into the bores of pipes so as to examine the walls of the pipes for defects, cracks or other discontinuities.
2. The Prior Art
The usual pipe inspection apparatus for examining, for example, gas pipelines, comprises a vehicle or a train of vehicles which are propelled along the pipeline by the gas flow in the pipeline. In one arrangement, ultrasonic transducers are mounted in a number of wheels (usually referred to as "wheel probes") which are urged into contact with the wall of the pipe. In use, ultrasound generated by the transducers is transmitted across the interface between the wheel probe and the wall of the pipe into the pipe wall. Ultrasound reflected or refracted from within the pipe wall is in turn received by the transducers within the wheels and subsequently analyzed.
In co-pending U.S. Pat. Application Ser. No. 933,031, filed Aug. 11, 1978, now abandoned there is described a wheel probe for insertion into the bore of a pipe for the purpose of ultrasonically inspecting the wall of the pipe. The wheel probe comprises a solid annular rim made of a non-deformable material (through which sound will pass) and side members, the side members and the rim defining a hollow chamber in which is contained a liquid acoustic coupling medium through which ultrasound will pass. One or more ulrasonic transducers are located within the chamber and are positioned adjacent the inside surface of the rim for directing and receiving sound through the rim, as well as a solid, resilient tire member mounted on the outside surface of the rim.
However, it has been found that in the highly pressurized gas environment of a gas pipeline, the seals used in the probe wheels for maintaining the probe wheel chamber fluid tight have failed, with consequent loss of the liquid acoustic coupling medium and the formation of large bubbles in the liquid which interfers with the passage of ultrasound. Furthermore, the wheel construction must have sufficient strength to withstand the pressure; this not only increases the weight of the probe, but also reduces the passage of ultrasound due to increased thickness of the probe wheel rim.
An object of the present invention is to provide an improved wheel probe designed to remedy the aforesaid disadvantages and limitations of known wheel probes.